Lens for reading an original, method and apparatus for reading an original, and image forming apparatus

ABSTRACT

A lens for reading an original, comprises five lenses as a whole including two positive and two negative lenses, an aspherical surface provided on at least one surface of the five lenses, a construction of four lens groups for five lenses which include a cemented lens constructed by cementing one of the positive lenses and one of the negative lenses, an aperture stop disposed between a second and third lens groups, and the cemented lens disposed adjacent to the aperture stop.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 10/633,724, filed Aug. 5, 2003, and claims priority to JapanesePatent Application No. 2002-226928, filed Aug. 5, 2002. The contents ofco-pending application Ser. No. 10/633,724 are incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens for reading an original, amethod and an apparatus for reading an original, and an image formingapparatus.

2. Description of the Prior Art

Conventionally, an apparatus for reading an original has been widelyutilized as an original reading unit of a facsimile machine and adigital copying machine, and an image scanner. The apparatus reduces anoriginal image to be read by a lens for reading an original, andconverts the original image to a signal by imaging it on a line sensorof a CCD or the like.

When a color original image is read out with a full-color, a 3-line CCDin which a light receiving element having a filter for decomposingcolors for red, green, and blue is disposed in three lines on one chipis used, and the color original image is imaged on a light receivingsurface of the light receiving element, then the color original image isdiscomposed into the three primary colors by the filter to convert it toa signal.

Comparing to a photographing lens, for the lens for reading an originalused for the device for reading an original, generally, a high contrastin a high spatial frequency area and a substantially 100% of an apertureefficiency until a peripheral portion of a filed angle are required.Moreover, a bright lens in order to achieve a high-speed reading is alsodemanded.

In order to read the original image accurately, for the lens for readingan original, a number of aberrations should be successfully corrected.

Especially, a distortion is relatively allowed for the photographinglens; however, the distortion should be sufficiently corrected for thelens for reading an original.

In order to read successfully color image information with thefull-color, a chromatic aberration for each color as well as a curratureof filed should be highly sufficiently corrected because an image of theoriginal image by the lens for reading an original is required to beimaged by coinciding an image-forming position of red, green, and bluetoward an optical axis on the light receiving surface of the 3-line CCD.

As the lens for reading an original, a Gauss type of four groups for sixlenses has been widely known in the prior art (for example, JapanesePatent Laid-Open Hei6-109971, Hei10-68881, Hei10-253881, andHei11-109221)

Generally, the Gauss type lens is capable of successfully correcting thecurrature of field up to about 20 degree of a half filed angle, andreducing a generation of a coma flare even though an aperture isrelatively large. As a result, the high contrast in the high spatialfrequency area until the peripheral portion of the image surface is ableto be received. However, the Gauss type is composed of 6 lenses, whichis a lot of numbers of lenses, and contributes to a large externaldiameter of lens. As a result, it becomes difficult for the lens forreading an original to miniaturize, and also there is a limit forminiaturizing and lowering a cost for the device for reading an originaland the image forming apparatus.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a lensfor reading an original (hereinafter calls an original reading lens),which meets a plurality of needs requiring for the lens for reading anoriginal such that a F/No is bright about 4.4 to 5.0, an apertureefficiency is substantially 100% until a peripheral portion, aberrationsare successfully corrected, a high contrast in a high spatial frequencyarea is included, and the lens is capable of corresponding to read afull-color original image, although a number of a construction of a lensis small such as four lens groups for five lenses, which is anadvantageous for miniaturizing and lowering a cost. The presentinvention has another object to provide a method for reading anoriginal, a device for reading an original, and an image formingapparatus by use of this lens for reading an original.

The present invention is characterized that it is constructed by fivelenses having at least two positive and two negative lenses. At leastone plane is an aspherical surface. A construction of the lens is thefour lens groups for the five lenses having a cemented lens constructedby cementing one lens of the positive lens and one lens of the negativelens. An aperture stop S is disposed between a second lens and a thirdlens groups. The cemented lens is disposed adjacent to the aperture stopS.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining a construction of a lens for a firstembodiment.

FIG. 2 is a view for showing some aberrations for the first embodiment.

FIG. 3 is a view for explaining a construction of a lens for a secondembodiment.

FIG. 4 is a view for showing some aberrations for the second embodiment.

FIG. 5 is a view for explaining a construction of a lens for a thirdembodiment.

FIG. 6 is a view for showing some aberrations for the third embodiment.

FIG. 7 is a view for explaining a construction of a lens for a fourthembodiment.

FIG. 8 is a view for showing some aberrations for the fourth embodiment.

FIG. 9 is a view for explaining a construction of a lens for a fifthembodiment.

FIG. 10 is a view for showing some aberrations for the fifth embodiment.

FIG. 11 is a view for explaining a construction of a lens for a sixthembodiment.

FIG. 12 is a view for showing some aberrations for the sixth embodiment.

FIG. 13 is view for explaining a construction of a lens for a seventhembodiment.

FIG. 14 is a view for showing some aberrations for the seventhembodiment.

FIG. 15 is a view for explaining one embodiment of an apparatus forreading an original.

FIG. 16 is a view for explaining one embodiment of an image formingapparatus.

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

Seven examples will be described below as examples of embodiments for anoriginal reading lens. The embodiments 1 to 4 are examples of a firstoriginal reading lens. The first original reading lens is provided witha cemented lens, which is composed of a third lens L3 and a fourth lensL4, and also satisfies any of a condition (1-1)˜(3-1) or a condition(1-2)˜(3-2).

In order to avoid a complication, in FIGS. 1,3,5,7,9,11, and 13, about afirst to a fourth lens groups reference numerals I to IV are usedcommonly regardless of constitutions of the lenses, and referencenumerals L1 to L5 are used commonly regardless of the specific lensforms about a first lens and a fifth lens.

In FIGS. 1,3,5,7,9,11, and 13, a CG1 denotes a contact glass and a CG2denotes a cover glass of a CCD. The CCD line sensor is a 3-line CCDhaving a color filter for decomposing a color, and is assumed that asize of a light receiving element is 10 μm and 600 dpi.

FIG. 1 shows a construction of a first embodiment and FIG. 3 shows aconstruction of a second embodiment. FIG. 5 shows a construction of athird embodiment and FIG. 7 shows a construction of a fourth embodiment.

The embodiments 5 to 7 are examples for a second original reading lens.The second original reading lens is provided with a cemented lens lens,which is composed of a second lens L2 and a third lens L3, and at leastone plane of the fourth lens L4 is adopted as an aspherical surface, andthe second original reading lens satisfies conditions (1-3)˜(3-3).

The embodiment 7 is an example of a third original reading lens. Thethird original reading lens has an aspherical surface for a convex lensface of the fourth lens L4 in the second original reading lens.

In the each embodiment, all lenses are glass lenses, and the asphericalsurface is formed by a glass mold.

Meanings of symbols in the each embodiment are as follows.

-   f: a combined focal length of an e line of an entire lens system.-   F: a F-number-   m: a reduced magnification-   Y: an object height-   ω: s half field angle-   r: s curvature radius of each surface (including an aperture stop)    from a contact glass to a CCD cover glass.-   d: s surface separation of the above mentioned each surface.-   nd: a refractive index of a d line-   νd: an Abbe's number-   ne: a refractive index of an e line-   f1: a focal length of an e line of the first lens-   n    an average of a nd of a lens including a positive refracting power-   n    an average of a nd of a lens including a negative refracting power-   ν    an average of a νd of a lens including a positive refracting power-   ν    an average of a νd of a lens including a negative refracting power    Left side sections in tables showing data of each embodiment are    indicators showing each surface. C1 and C2 show surfaces of an    object side and an image side of a contact glass, 1 to 10 show each    surface (a surface of a lens and a surface of an aperture stop)    counting from an object side of a original reading lens, and C3 and    C4 show surfaces of an object side and an image side of a CCD cover    glass.

The aspherical surface is shown by a known formula below.X=1/RY ²/[1+√{square root over ( )}[{1−1+KY/R ² }+A4·Y4+A6·Y ⁶ +A8·Y ⁸+A10·Y ¹⁰]

In the above mentioned formula

-   X: a distance form a tangent plane in an apex of an aspherical    surface of the aspherical surface in a height Y from an optical    axis.-   Y: a height from an optical axis-   R: a curvature radius of a paraxial of an aspherical surface-   K: a conical constant-   A4, A6, A8, A10: an aspherical coefficient in numerical values, for    example [E-06] means [10⁻⁶]    First Embodiment

FIG. 1 shows a construction of a lens of the first embodiment. Theoriginal reading lens of FIG. 1 has a first to a fourth lens groupssequentially arranged from an object side (a left side of FIG. 1); thefirst lens group I is composed of a first lens L1 having a positiverefracting power; the second lens group II is composed of a second lenshaving a negative refracting power; an aperture stop S is disposedbetween the second lens group and the third lens group; the third lensgroup III having a positive refracting power is composed of a cementedlens, which is constructed by cementing a third lens L3 and a fourthlens L4; and the fourth lens group IV is composed of a fifth lens L5having a positive or a negative refracting power.

In this original reading lens, the cemented lens is constructed by thethird and the fourth lenses. The third lens L3 is a positive lens andthe fourth lens L4 is a negative lens. The fifth lens L5 is a negativelens.

As showing in FIG. 1, in this original reading lens, the first lens L1is a positive meniscus lens arranging a convex face directed to theobject side. The second lens L2 is a negative meniscus lens arranging aconcave face directed to the object side. Moreover, at least one surfaceof the first lens L1 is able to be the aspherical surface.

The third lens L3 as the positive lens in particular is a positivemeniscus lens arranging a concave face directed to the object side. Thefourth lens L4 as the negative lens in particular is a negative meniscuslens arranging a concave face directed to the object side. The cementedlens in FIG. 1 has the positive refracting power.

(A Second Construction Example of the Cemented Lens)

The cemented lens of the above original reading lens is able to beconstructed that the third lens L3 is the negative lens and the fourthlens L4 is the positive lens as showing the example in FIG. 7. The thirdlens L3 of the negative lens constructing the cemented lens inparticular is able to be a double-concave lens (FIG. 7), and the fourthlens L4 of the positive lens is able to be a double-convex lens (FIG.7).

(A Construction of the Fifth Lens)

The fifth lens L5 as the negative lens in the above original readinglens is the negative meniscus lens having the convex face directed tothe object side.

(A First Condition of the Original Reading Lens)

In this original reading lens, a combined focal length f with respect toan e line of an entire lens system, a focal length f1 with respect to ane line of the first lens counted from the object side, averages n

and n

of positive and negative lenses in a refractive index with respect to ad line of a lens material, and averages of ν

and ν

of positive and negative lenses of an Abbe's number of a lens materialsatisfy following conditions.0.3<f 1 /f<1.2  (1-1)−0.18<n

·n

<0.18  (2-1)0.88<ν

−ν

<35.0  (3-1)

The aforementioned n

is the average of the refractive index of each material for two or threepositive lenses, which are included in the five lenses. In other word,provided the number of the positive lens as Np (=2 or 3), and when therefractive index of the material of these positive lenses is adopted asn

i (i=1˜Np), n

is defined as n

=Σn

i/Np. In n

provided the number of the negative lens in the five lenses as Np (=2 or3), when the refractive index of material of each negative lens isadopted as n

j (j=1˜Nn), n

is defined as n

=Σn

j/Nn. ν

and ν

are defined as ν

=Σν

i/Np and ν

=Σν

j/Nn as well. ν

i and ν

j are the Abbe's number of the material of each positive and negativelens, and a sum is conducted about the above i and j.

The above condition (1-1) is to determine a power of the first lensgroup with respect to the entire lens system. The original reading lensis an optical system in which a real image is imaged. Therefore, thefocal length f of the entire lens system is a positive, and a focallength f1 of the first group is positive under the condition (1-1).

If the power exceeds 1.2, which is an upper limit of the condition(1-1), the power of the first lens group becomes too weak, and as aresult, the positive lens constructing the first lens group becomes toobig, and it results in increasing a cost. Moreover, if the power exceeds0.3, which is a lower limit of the condition (1-1), it is advantageousfor downsizing the original reading lens, but a coma flare becomeslarger.

As described above, this original reading lens is constructed by fourlens groups for five lenses, and the aperture stop is arranged betweenthe second lens group and the third lens group. The cemented lens isdisposed adjacent to this aperture stop. The cemented lens is cementedby the positive and the negative lenses.

When image information of an original is read, a requirement forcorrecting a distortion is strict. However, in the original reading lensof this embodiment, the aperture stop is arranged between the second andthe third lens groups, and the cemented lens is disposed adjacent tothis aperture stop. Moreover, by the above conditions (1-1), (2-1), and(3-1), a distribution of the power in the vicinity of the aperture stopis successfully balanced, and the strict requirement for correcting theabove distortion is satisfied. A chromatic aberration is alsosuccessfully collected by use of the cemented lens.

(A Second Condition of the Original Reading Lens)

In the above described original reading lens, a further favorableoptical performance is able to be achieved in such a manner that theabove f, f1, n

, n

, ν

, and ν

satisfy following conditions.0.40<f 1 /f<0.57  (1-2)0.08<n

·n

<0.14  (2-2)3.47<ν

·ν

<19.49  (3-2)

The above mentioned condition (2-1) is to decide a range of therefractive index of the

lens and

lens constructing the original reading lens. If the refractive indexexceeds 0.18 of an upper limit, the refractive index as an entire

lens becomes much bigger than the refractive index as an entire

lens, and Petzval's sum becomes too small. As a result, the imagesurface is inclined to a positive side and, and a curvature becomes big.On the other hand, if the refractive index exceeds −0.18 of a lowerlimit, Petzval's sum becomes too big. As a result, the image surface isinclined to the negative side, and astigmatism becomes larger.Therefore, a favorable performance of imaging in an entire screenbecomes difficult to be received beside the range of the condition(2-1).

The original reading lens can achieve a further favorable performance bysatisfying the conditions (1-2)˜(3-2) in which the conditions areslightly narrower than the above conditions (1-1)˜(3-1).

Table 1 shows data of the first embodiment.

TABLE 1 f = 80.404, F = 4.36, m = 0.23622, Y = 152.4, ω = 19.9° r d ndνd ne c1 0.000 3.200 1.51680 64.2 1.51872 c2 0.000 1 28.366 7.3851.76800 49.2 1.77172 2 152.845 0.100 3 94.484 4.994 1.60398 34.471.60813 4 19.183 12.664 5 0.0 8.665 (aperture stop) 6 −581.430 10.0001.81600 46.6 1.82016 7 −21.428 10.000 1.64769 33.84 1.65222 8 −94.7960.100 9 50.767 8.383 1.84700 23.8 1.85540 10 42.885 c3 0.000 1.0001.51680 64.2 1.51872 c4 0.000

Table 2 shows a conical constant and an aspherical coefficient of anaspherical surface for the first embodiment.

TABLE 2 < aspherical coefficient > surface number K A4 A6 A8 A10 1−0.53613 9.4038E−07 1.8022E−09 −7.165E−12 8.33E−15

Table 3 shows values of parameters of each condition in the firstembodiment.

TABLE 3 < values of condition formulas > Item Value f1 43.995 f1/f 0.547n

− n

0.092 ν

− ν

17.20

As describing in table 3, the original reading lens of the firstembodiment satisfies the above conditions (1-1), (2-1), and (3-1) andthe conditions (1-2), (2-2), and (3-2).

FIG. 2 shows a view for some aberrations about the first embodiment.

In a view of a spherical aberration, a dotted line shows a sincondition. In a view of astigmatism, solid lines show sagittal rays, anddotted lines show meridional rays. e shows e line (546.07 nm), g shows ag line (436.83 nm), c shows c line (656.27 nm), and F shows F line(486.13 nm). These are the same views for the same aberrations for otherembodiments from 2 to 7.

Second Embodiment

FIG. 3 shows a construction of a lens for the second embodiment. Theoriginal reading lens as describing in FIG. 3 has a first to a fourthlens groups sequentially arranged from an object side; a first lensgroup I is composed of a first lens L1 having a positive refractingpower; a second lens group II is composed of a second lens L2 having anegative refracting power; an aperture stop S is disposed between thesecond and the third lens groups; a third lens group III having apositive refracting power is composed of a cemented lens, which areconstructed by cementing a third lens L3 and a fourth lens L4; and afourth lens group IV is composed of a fifth lens L5.

In the cemented lens of the third lens group III, the third lens L3 is apositive lens and the fourth lens L4 is a negative lens. The fifth lensL5 is a negative lens.

In the original reading lens of FIG. 3, the first lens L1 is a positivemeniscus lens arranging a convex face directed to the object side.Moreover, at least one surface of the first lens L1 is able to be anaspherical surface. The second lens L2 can be a negative meniscus lensarranging a concave face directed to the object side.

The third lens L3 as the positive lens is able to be a positive meniscuslens arranging a convex face directed to the object side. The fourthlens as the negative lens is able to be a negative meniscus lensarranging a concave face directed to the object side. In this case, thecemented lens of the third lens group III has the positive refractingpower.

The fifth lens L5 in the original reading lens of FIG. 3 is able to be anegative meniscus lens arranging a convex face directed to the objectside as showing in FIG. 3.

Table 4 shows data in the second embodiment.

TABLE 4 f = 80.643, F = 4.96, m = 0.23622, Y = 152.4, ω = 19.9° r d ndνd ne c1 0.000 3.200 1.51680 64.2 1.51872 c2 0.000 1 24.816 6.7751.74330 49.33 1.74689 2 620.577 0.100 3 168.619 1.500 1.59551 39.221.59911 4 16.188 7.297 5 0.0 4.142 (aperture stop) 6 −225.417 9.3821.71300 53.94 1.71615 7 −14.284 3.993 1.54814 45.82 1.55098 8 −73.8040.100 9 90.254 9.412 1.64769 33.84 1.65222 10 60.644 c3 0.000 1.0001.51680 64.2 1.51872 c4 0.000

Table 5 shows a conical constant and an aspherical coefficient of anaspherical surface.

TABLE 5 < aspherical coefficient > surface number K A4 A6 A8 A10 1−0.58442 −5.4490E−07 −7.06818E−09 −1.70944E−11 −1.00091E−14

Table 6 shows values of parameters of conditions in the secondembodiment.

TABLE 6 < values of conditions formulas > Item Value f1 34.443 f1/f0.427 n

− n

0.118 ν

− ν

5.76

As shown in FIG. 6, the original reading lens of the second embodimentsatisfies the above conditions (1-1),(2-1), and (3-1) and the conditions(1-2),(2-2), and (3-2).

FIG. 4 shows a view for some aberrations in the second embodiment.

(Third Embodiment)

FIG. 5 shows a construction of a lens of the third embodiment. Theoriginal reading lens shown in FIG. 5 has a first to a fourth lensgroups sequentially arranged from an object side (a left side of FIG.5); the first lens group I is composed of the first lens L1 having apositive refracting power; the second lens group II is composed of thesecond lens L2 having a negative refracting power; the aperture stop Sis disposed between the second and the third lens groups; the third lensgroup III having a positive refracting power is composed of a cementedlens, which is constructed by cementing a third lens L3 and a fourthlens L4; and the fourth lens group IV is composed of the fifth lens L5having a positive or a negative refracting power.

In the original reading lens in FIG. 5, the first lens L1 is able to bea positive meniscus lens arranging a convex face directed to the objectside, and the second lens L2 is able to be a negative meniscus lensarranging a convex face directed to the object side. Moreover, in theoriginal reading lens, at least one surface of the first lens L1 is ableto be an aspherical surface.

In the FIG. 5, the third lens L3 constructing the cemented lens of thethird lens group III is the positive lens, and the fourth lens L4 is thenegative lens. The third lens L3 as the positive lens is set to be adouble-convex lens. The fourth L4 as the negative lens is set to be adouble-concave lens. In this case, the cemented lens of the third lensgroup III has the positive refracting power.

The fifth lens L5 in FIG. 5 is set to be a positive meniscus lensarranging a concave face directed to the object side.

Table 7 shows data of the third embodiment.

TABLE 7 f = 81.503, F = 4.96, m = 0.23622, Y = 152.4, ω = 19.7° r d ndνd ne c1 0.000 3.200 1.51680 64.2 1.51872 c2 0.000 1 23.142 6.3401.78881 41.63 1.79331 2 70.027 0.100 3 50.803 2.070 1.64510 31.351.64997 4 15.872 13.179 5 0.0 5.919 (aperture stop) 6 115.786 6.1801.80901 39.52 1.81387 7 −16.873 9.346 1.64769 33.84 1.65222 8 67.8733.927 9 −104.080 4.959 1.71300 53.9 1.71615 10 −52.467 c3 0.000 1.0001.51680 64.2 1.51872 c4 0.000

Table 8 shows a conical constant and an aspherical coefficient of anaspherical surface.

TABLE 8 < aspherical coefficient > surface number K A4 A6 A8 A10 1−0.47345 2.37697E−06 5.34943E−09 −1.17279E−11 2.60656E−14 6 −11.0046−8.63490E−07   −1.47483E−08     1.29599E−10 −5.45254E−13  

Table 9 shows values of parameters of conditions in the thirdembodiment.

TABLE 9 < values of conditions formulas > Item Value f1 41.112 f1/f0.504 n

− n

0.109 ν

− ν

11.83

As shown in FIG. 9, the original reading lens of the third embodimentsatisfies the above conditions (1-1), (2-1), and (3-1), and theconditions (1-2), (2-2), and (3-2).

FIG. 6 shows a view for some aberrations in the third embodiment.

(Fourth Embodiment)

FIG. 7 shows a constitution of a lens of the fourth embodiment. Theoriginal reading lens of FIG. 7 has a first to a fourth lens groupssequentially arranged from an object side; the first lens group I iscomposed of the first lens L1 having a positive refracting power; thesecond lens group II is composed of the second lens L2 having a negativerefracting power; an aperture stop S is disposed between the second andthe third lens groups; the third lens group III having a positiverefracting power is composed of a cemented lens, which is constructed bycementing the third lens L3 and the fourth lens L4; and the fourth lensgroup is composed of the fifth lens L5 having a negative refractingpower.

In this original reading lens, the cemented lens is constructed by thethird lens L3 and the fourth lens L4. The third lens L3 is a negativelens composed of a double-concave lens and the forth lens L4 is apositive lens composed of a double-convex lens. The cemented lens of thethird group III has the positive refracting power. The fifth lens L5 isthe negative lens.

In the original reading lens of FIG. 7, in particular, the first lens L1is able to be a positive meniscus lens arranging a convex face directedto the object side. The second lens L2 is able to be a negative meniscuslens arranging a convex face directed to the object side. Moreover, inthe above mentioned original reading lens, at least one surface of thefirst lens L1 is able to be an aspherical surface.

Table 10 shows data of the fourth embodiment.

TABLE 10 f = 81.814, F = 4.46, m = 0.23622, Y = 152.4, ω = 19.6° r d ndνd ne c1 0.000 3.200 1.51680 64.2 1.51872 c2 0.000 1 29.118 10.0001.81661 45.7 1.82086 2 271.007 0.100 3 74.199 1.500 1.70285 32.611.70795 4 19.049 8.347 5 0.0 9.502 (aperture stop) 6 −36.761 1.5001.59300 35.5 1.59696 7 54.704 6.927 1.81600 46.6 1.82016 8 −33.591 0.1009 34.759 1.500 1.82666 34.84 1.83228 10 31.560 c3 0.000 1.000 1.5168064.2 1.51872 c4 0.000

Table 11 shows a conical constant and an aspherical coefficient anaspherical surface.

TABLE 11 < aspherical coefficient > surface number K A4 A6 A8 A10 1−0.61636 1.83234E−07 1.51715E−09 −1.87652E−11 3.0198E−14

Table 12 shows values of parameters of conditions in the fourthembodiment.

TABLE 12 < values of condition formulas > Item Value f1 39.016 f1/f0.477 n

− n

0.131 ν

− ν

12.01

As shown in table 12, the original reading lens of FIG. 7 satisfies theabove conditions of lens (1-1), (2-1), and (3-1), and conditions of lens(1-2), (2-2), and (3-2).

FIG. 8 shows a view for some aberrations in the fourth embodiment.

(Fifth Embodiment)

FIG. 9 shows a lens constitution of an original reading lens in thefifth embodiment.

The original reading lens of the fifth embodiment shown in FIG. 9 has afirst to a fourth lens groups sequentially arranged from an object side;a first lens group I is composed of a first lens L1 having a positiverefracting power; a second lens group II having a negative refractingpower is composed of a cemented lens, which is constructed by cementinga second lens L2 having a positive refracting power and a third lens L3having a negative refracting power; an aperture stop S is disposedbetween the second and the third lens groups; a third lens group III iscomposed of a fourth lens L4 having a negative refracting power; and afourth lens group IV is composed of a fifth lens L5 having a positiverefracting power.

The original reading lens as shown in FIG. 9 is different from theoriginal reading lens as shown in FIG. 1 in that the second lens groupII is constructed by the cemented lens having the negative refractingpower, and the fourth lens L4 of the third lens group III has thenegative refracting power.

When the second lens group of the original reading lens is adopted asthe cemented lens, the second lens L2 and the third lens L3 composingthe cemented lens of the second lens are able to be meniscus lensesarranging convex faces directed to the object side as showing FIGS.9,11, and 13.

In the original reading lens as shown in FIG. 9, at least one surface ofthe fourth lens L4 is able to be an aspherical surface.

In the original reading lens shown in FIG. 9, if the above mentioned f,f1, n

, n

, ν

, and ν

satisfy the following conditions, a further successful opticsperformance is able to be achieved.0.54<f 1 /f<1.14  (1-3)−0.16<n

−n

0.05  (2-3)18.11<ν

−ν

<32.13  (3-3)

The above mentioned condition (3-1) is the condition for correcting achromatic aberration on an axis. If the condition exceeds 35.0 of anupper limit, the chromatic aberration on the axis is over corrected, andthe chromatic aberration on the axis becomes large to a positive side ina short wavelength side than a dominant wave length. If the conditionexceeds 0.88 of a lower limit, the chromatic aberration on the axisbecomes large to a negative side in the short wavelength side than thedominant wave length.

When the original reading lens has the second lens as the cemented lensand the convex face of the fourth lens as the aspherical surface, asconditions to have a successful performance for imaging with a compactand a low cost, a further successful performance is able to be receivedby satisfying conditions of (1-3)˜(3-3), which is the slight narrowerconditions than the conditions (1-1)˜(3-1).

Table 13 shows data of the fifth embodiment.

TABLE 13 f = 84.532, F = 5.01, m = 0.23622, Y = 152.4, ω = 19.0° r d ndνd ne c1 0.000 3.200 1.51680 64.2 1.51872 c2 0.000 1 31.051 6.4031.83400 37.3 1.83930 2 93.332 3.269 3 30.621 4.787 1.48700 70.4 1.488664 475.204 1.500 1.70959 27.97 1.71559 5 20.376 7.645 6 0.0 12.193(aperture stop) 7 −14.634 5.433 1.84700 23.8 1.85540 8 −20.700 0.100 9−130.896 6.825 1.62286 60.34 1.62533 10 −29.219 c3 0.000 1.000 1.5168064.2 1.51872 c4 0.000

Table 14 shows a conical constant and an aspherical coefficient anaspherical surface.

TABLE 14 < aspherical coefficient > surface number K A4 A6 A8 A10 70.22916 5.60667E−06 1.22914E−07 −9.83972E−10 7.57302E−12

Table 15 shows values of parameters of conditions in the embodiment 5.

TABLE 15 < values of conditions formulas > Item Value f1 52.956 f1/f0.626 n

− n

−0.130 ν

− ν

30.13

FIG. 10 shows a view for some aberrations in the fifth embodiment.

(Sixth Embodiment)

In FIG. 11 shows a constitution of a lens of the sixth embodiment. Aoriginal reading lens as shown in FIG. 11 has a first to a fourth lensgroups sequentially arranged from an object side; the first lens group Iis composed of the first lens L1 having a positive refracting power; asecond lens group II having a negative refracting power is composed of acemented lens, which is constructed by cementing a second lens L2 havinga positive refracting power and a third lens L3 having a negativerefracting power; an aperture stop S is disposed between the second andthe third lens groups; a third lens group III is composed of a fourthlens L4 having a negative refracting power; and a fourth lens group IVis composed of a fifth lens L5 having a positive refracting power.

The original reading lens shown in FIG. 11 is different from theoriginal reading lens shown in FIG. 1 in that the second lens group IIis constructed by the cemented lens having the negative refractingpower, and the fourth lens L4 of the third lens group III has thenegative refracting power.

The second lens L2 and the third lens L3, which construct the cementedlens of the second lens group of FIG. 11, are meniscus lenses arrangingconvex faces directed to the object side.

Moreover, in the original reading lens as shown in FIG. 11, at least onesurface of the fourth lens L4 is able to be an aspherical surface.

The original reading lens as shown in FIG. 11 satisfies the abovementioned conditions (1-3),(2-3), and (3-3). Effects to satisfy theseconditions are as described as the original reading lens of FIG. 9.

Table 16 shows data of the sixth embodiment.

TABLE 16 f = 84.431, F = 5.06, m = 0.23622, Y = 152.4, ω = 19.0° r d ndνd ne c1  0.000 3.200 1.51680 64.2 1.51872 c2  0.000 1  32.681 5.0051.80557 39.85 1.81037 2  55.578 0.479 3  24.784 7.269 1.76737 44.281.77149 4 366.816 1.500 1.64068 31.64 1.64547 5  13.947 9.985 6 0.04.445 (aperture stop) 7 −34.570 4.505 1.68893 31.16 1.69416 8 −78.8597.608 9 −172.041 10.000 1.48700 70.4 1.48866 10 −22.788 c3  0.000 1.0001.51680 64.2 1.51872 c4  0.000

Table 17 shows a conical constant and an aspherical coefficient of thesixth embodiment.

TABLE 17 < aspherical coefficient > surface number K A4 A6 A8 A10 8−5.09883 8.00906E−06 1.09569E−08 −8.25047E−11 3.25340E−13

Table 18 shows values for parameters of conditions in the sixthembodiment.

TABLE 18 < values of condition formulas > Item Value f1 89.162 f1/f1.056 n

− n

0.022 ν

− ν

20.11

FIG. 12 shows a view for some aberrations in the sixth embodiment.

(Seventh Embodiment)

FIG. 13 shows a construction of a lens in the seventh embodiment. Theoriginal reading lens in FIG. 13 has a first to a fourth lens groups assame as the original reading lens in FIG. 9 sequentially arranged froman object side; the first lens group I is composed of a first lens L1having a positive refracting power; the second lens group II having anegative refracting power is composed of a cemented lens, which isconstituted by cementing a second lens L2 having a positive refractingpower and a third lens L3 having a negative refracting power; theaperture stop S is disposed between the second and the third lensgroups; a third lens group III is composed of a fourth lens L4 having anegative refracting power; and a fourth lens group IV is composed of afifth lens L5 having a positive refracting power.

The second lens L2 and the third lens L3, which construct the cementedlens of the second lens group, is a meniscus lenses arranging convexfaces directed to the object side. In the original reading lens as shownin FIG. 13, at least one surface of the fourth lens L4 is able to be anaspherical surface.

In the embodiment 7, the aspherical surface is formed on the convex lensface of the fourth lens L4. As showing FIG. 13, the fourth lens L4 has asmall diameter adjacent to the aperture stop S. The aspherical plane ofthe convex lens face of this fourth lens L4 is easy to be formed by aglass mold. Therefore, it is possible to lower a cost of the asphericalsurface lens, and also it is effective for lowering a cost of theoriginal reading lens. The original reading lens of FIG. 13 satisfiesthe above mentioned conditions (1-3),(2-3), and (3-3). The effects tosatisfy these conditions are as mentioned above.

Table 19 shows data of the seventh embodiment.

TABLE 19 f = 84.285, F = 4.95, m = 0.23622, Y = 152.4, ω = 19.1° r d ndνd ne c1 0.000 3.200 1.51680 64.2 1.51872 c2 0.000 1 29.667 5.7771.71300 53.94 1.71615 2 58.075 0.100 3 23.951 7.719 1.72342 37.991.72793 4 3743.417 1.500 1.67270 32.17 1.67764 5 12.917 8.853 6 0.05.980 (aperture stop) 7 −29.479 1.500 1.68893 31.16 1.69416 8 −55.5855.280 9 −128.284 10.000 1.48749 70.44 1.48914 10 −19.790 c3 0.000 1.0001.51680 64.2 1.51872 c4 0.000

Table 20 shows a conical constant and an aspherical coefficient anaspherical surface of the seventh embodiment.

TABLE 20 < aspherical coefficient > surface number K A4 A6 A8 A10 8−8.35253 5.89609E−06 1.95474E−08 −4.66956E−11 1.51034E−13

Table 21 shows values of parameters of conditions in the seventhembodiment.

TABLE 21 < values of conditions formulas > Item Values f1 78.060 f1/f0.926 n

− n

−0.040 ν

− ν

22.46

FIG. 14 shows a view for some aberrations about the seventh embodiment.

In the above described every embodiments 1 to 7, as showing each view ofFIGS. 2,4,6,7,8,10,12, and 14, the lenses have a blight F-number ofabout F/No 4.4 to 5.0. An aperture efficiency is practically 100% untila peripheral portion of an image. A plurality of aberrations issuccessfully collected, and a high contrast in a high spatial frequencyarea is included. Moreover it is possible to correspond appropriately toread an image with a full-color.

The original reading lenses in the embodiments 1 to 7 use glass lensesfor all five lenses, and it is possible to form the aspherical surfaceby use of the glass mold. When forming the aspherical surface by theglass mold, it is preferable to form the convex lens face in terms of aneasiness of forming. Moreover, the original reading lenses of theembodiments 1 to 7 use the glass lenses for all the five lenses, and itis possible to form the aspherical surface on the convex lens face ofthe fourth lens by the glass mold.

In the above mentioned every original reading lens, a temperature istend to be raised by an influence of a heat of a lamp for illuminatingan original. In order to have a stable performance with respect to thesetemperature fluctuations, it is better for the first to the fifth lensesL1 to L5 to have the glass lenses. In this case, it is better to formthe aspherical surface by use of the glass mold.

The original reading lenses of the above embodiments 1 to 7 are able tobe applied to a device for reading an original and an image formingapparatus. This device for reading an original is able to be constructedby use of any one of the original reading lens shown in the embodiments1 to 7. The original reading lens, which includes an illumination systemto illuminate an object, an image-forming lens to reduce and image areflected light by the original illuminated by this illumination system,and a line-sensor to conduct a photoelectric transfer for an image of anoriginal image imaged by this image-forming lens, is constructed by useof any one of the original reading lens shown in the embodiments 1 to 7as an image-forming lens.

This device for reading an original may be the device, which includes adevice or an element capable of decomposing a color on an optical pathof an optical system, and reads the original image with a full-color. Inother words, the device for reading an original is possible to have oneor a plurality of devices for decomposing a color or elements fordecomposing a color on the optical path of the optical system to readthe original image with the full-color. For example of a CCD or a CMOSimage sensor, which include a color filter, is able to be used as thisdevice for decomposing the color or the element for decomposing thecolor.

In this original reading lens, a method in which an original is disposedon a contact glass in plane; the original is illuminated in a slit likeshape, a reflected light from an illumination portion is reduced andimaged on a line sensor by the original reading lens; and in a directionperpendicular to the longitudinal direction of the illumination portionof the slit like shape, an illumination portion and an original arerelatively displaced and the original image is read by illuminating andscanning of a surface of the original is adopted. Therefore, any one ofthe lens described in the constitutions for arranging the lenses showingin the embodiments 1 to 7 and conditions (1-1) to (3-1) is able to beused.

In illuminating and scanning the surface of the original, this methodfor reading an original is capable of displacing the optical system byfixing the original. This method is able to be accomplished byconstructing any one of the original or the optical system or the bothrelatively transferable as transferring the original by fixing theoptical system.

About the illumination with respect to the original in this method forreading an original, it is preferable to illuminate that whenilluminating in the slit like shape with respect to the original on thecontact glass, a degree of illumination in an illumination portionincreases from a center portion of the slit toward both ends portion ofa longitudinal direction of the slit. By adopting this illuminatingmethod, it is possible to image an image, which has a small change ofthe degree of illumination in the longitudinal direction of the linesensor.

FIG. 15 shows an embodiment of an original reading lens having theoriginal reading lens described in FIGS. 1 to 14.

An original 2 is disposed to a contact glass 1, and illuminated in along slit like shape in a direction perpendicular to the view by anillumination optical system arranged under the contact glass 1. Thisillumination optical system (not shown) is constructed by a device of alamp illumination (for example a fluorescent) provided in a firstrunning body 3 as extending in the direction perpendicular to the viewof FIG. 15. However, it is possible to use a device for light scanningto illuminate a laser such as an image forming apparatus.

A reflected light by the illuminated original 2 is reflected on a firstmirror 3-a of the first running body 3. After that the light isreflected on a first mirror 4-a and a second mirror 4-b of a secondrunning body 4, and led to a original reading lens 5, then the light isimaged as a reduced small image on a line sensor 6 by the originalreading lens 5.

About a reading for the original 2, a constant optical path length,which exists from the surface of the original to the original readinglens, is maintained by moving the first running body 3 till a position3′ with a speed V, and at the same time, by moving the second runningbody 4 till a position 4′ with a speed V/2.

In other words, this original reading lens has the above illuminationoptical system to illuminate the original, a image-forming lens 5 forreducing and imaging the reflected light of the original by thisillumination optical system, and a line sensor 6 to conduct aphotoelectric transfer for the image of the original image imaged bythis image-forming lens, and it is the original reading lens, which usesany one of the original reading lens from FIGS. 1 to 14 as theimage-forming lens 5.

This original reading lens has a function for decomposing a color in theoptical path of the optical system, and is adopted to read imageinformation of the original with a full-color. In this embodiment, thedevice or the element for decomposing a color is constructed by the linesensor 6. This line sensor 6 is a 3-line CCD in which a light receivingelement having a filter for decomposing colors of R(red), G(green), andB(blue) is arranged in three lines in one chip. This line sensor 6carries out the decomposing the colors into three colors by forming acolor image on the surface of the received light. Therefore, it ispossible to read a color original with a full-color.

Beside the above mentioned device and element, a device for decomposinga color by inserting selectively a filter or a prism for decomposing acolor between the original reading lens 5 and the line sensor 6, adevice for illuminating an original by flushing sequentially threecolors light sources of R (red), G (green), and B (blue), and so on andsome known methods, devices, or elements are included as the devices orthe elements for decomposing a color.

In other words, in the original reading lens of FIG. 15, the method thatthe original 2 is put on the contact glass 1; the original 2 isilluminated in the slit like shape; the reflected light from theillumination portion is reduced and imaged on the line sensor 6 by theoriginal reading lens 5; and in the direction perpendicular to thelongitudinal direction of the illumination portion of the slit likeshape (horizontal directions of FIG. 15), the illumination portion andthe original are relatively displaced and the original image is read byilluminating and scanning the surface of the original is adopted. Thedevice utilizes any one of the original reading lens shown in FIGS. 1 to14 as the original reading lens.

The slit like shaped illumination with respect to the original 2 on thecontact glass 1 is carried out in such a manner that the degree ofillumination is increased toward the both end portion in thelongitudinal direction of the slit from the center of the slit in orderto equalize the brightness of the image of the original image on theline sensor 6 in the longitudinal direction of the sensor. Moreover acorrection of shading depending on needs is carried out in order toequalize the brightness of the image of the original image.

The original reading lens of the above mentioned embodiments 1 to 7 areable to apply to the device for reading an original and the imageforming apparatus. This image forming apparatus is the image formingapparatus in which the image information is imaged as the image, and hasany one of the above mentioned device for reading an original as thedevice for reading an original to read the original image in order tochange the original image into the image information. This image formingapparatus may be the apparatus, which conducts the image forming bywriting the image information into a photosensitive media with a lightscanning.

Consequently, this image forming apparatus has a device to write theimage information into the photosensitive media by the light scanning.Specifically, this image forming apparatus has a device that anelectrostatic latent image is written in a photoconductor with the lightscanning by use of a photoconductive photoconductor formed as a cylindershape, and a toner having a prescribed color is adhered to theelectrostatic latent image written in the photoconductor, then the colortoner of the photoconductor is fixed and visualized. This prescribedcolor is composed of a plurality of colors.

FIG. 16 shows one embodiment of an image forming apparatus.

This image forming apparatus has a device for reading an original 200and a laser printer of an image forming part 100. The device for readingan original 200 outputs the original image of the original 2 as anelectronic signal by the line sensor 6 in accordance with theconstruction and the operations as described in FIG. 15. The originalreading lens 5 is selected voluntarily from the above embodiments 1 to 7as the original reading lens.

The image forming part 100 has a photoconductive photoconductor 111formed in a cylinder shape as a photosensitive media. A periphery of thephotoconductor 111 is provided with an electrification roller 112 as anelectrification device, a development device 113, a transfer roller 114,and a cleaning device 115. A corona-charger is able to be used as theelectrification device.

Moreover, the image forming part 100 is provided with a light scanningdevice 117 to carry out the light scanning with a laser beam LB byreceiving image information from the line sensor 6, and is adapted toconduct an exposure by an optical writing between the electrificationroller 112 and the development device 113.

Reference numeral 116 denotes a fixing device, reference numeral 118 acassette, reference numeral 119 a pair of resist rollers, referencenumeral 120 a paper feeding, reference numeral 121 a transport path,reference numeral 122 a pair of ejection rollers, reference numeral 123a tray, and reference numeral P a transfer paper as a recording medium.

When the image forming is carried out, the photoconductor 111 of thephotoconductivity is rotated at a constant speed in clockwise in FIG.16, and the surface is equally charged by the electrification roller112, then the electrostatic latent image is formed by receiving theexposure by the optical writing of the laser beam LB of the lightscanning device 117. The formed electrostatic latent image is a negativelatent image, and the image part is exposed.

This electrostatic latent image is reversely developed by thedevelopment device 113, and the toner image is formed on thephotoconductor 111. The cassette 118 in which the transfer paper P iscontained is detachable to a body of the image forming apparatus 100,and as disposing in the view, one sheet of a top of the containedtransfer paper P is fed by the paper feeding 120, and the leading endportion of the transfer paper P is caught by the pair of the resistrollers 119.

The pair of the resist rollers 119 sends the transfer paper P to thetransfer part in timing with moving the toner image on thephotoconductor 111 to a transfer position. The sent transfer paper P isoverlapped with the toner image in the transfer part, and the tonerimage is electrostatic-transferred by an operation of the transferroller 114. The transfer paper P in which the toner image is transferredis sent to the fixing device 116, and the toner image is fixed in thefixing device 116, and ejected on the tray 123 by the pair of theejection rollers 122 through the transport path 121.

After the toner image is transferred, the surface of the photoconductor111 is cleaned by the cleaning device 115, and a residual of the toner,a powder of the paper, and so on are eliminated.

Consequently, the image forming apparatus in FIG. 16 is the imageforming apparatus to form the image information as the image, has thedevice for reading an original as the device for reading an original 200to read the original image in order to change the original image to theimage information, conducts the image forming by writing the imageinformation to the photoconductor 111 with the light scanning, uses thephotoconductive photoconductor 111 as a photosensitivity media so as tovisualizes the electrostatic latent image, which is written by the lightscanning, with the prescribed color of toner.

The image forming apparatus of FIG. 16 is to form an image of amonochrome; however, the device for reading an original 200 is able toconduct the reading for an original with a full-color. For example, acolor image is able to be formed by carrying out as follows.

In other words, instead of the development device 113, by use of a knownrevolver type development device in connection with a color imageforming apparatus, the photoconductor 111 is formed with anelectrostatic latent image in which each image information (yellow,magenta, cyan-color image information) decomposed into R, G, and B andblack image information are sequentially written and corresponded, andthese are visualized by each color of toner such as yellow, magenta,cyan, and black. The color image which is produced by this istransferred and fixed on the transfer paper P.

In this case, the toner image of the above each color is sequentiallyformed on the photoconductor 111, and the toner image is transferred toan intermediate transfer media (transfer belt, and so on) at every timeforming the toner image, then the toner image is possible to betransferred to the transfer paper after forming the color image byoverlapping on the intermediate transfer media. Moreover, it is possiblefor an image forming part to be constructed as the know tandem imageforming part of electro-photography process.

As described above, the novel original reading lens, the method and thedevice for reading an original, and the image forming apparatus are ableto be accomplished by the present invention.

As being apparent from the views for some aberrations of eachembodiment, in the lens for reading the original of this invention,regardless of small number of lenses such as the four groups for thefive lenses, F-number is the relatively large aperture such as 4.4 to5.0, the aperture efficiency is practically 100%, the reducedmagnification is about 0.236, the chromatic aberration is preferablycorrected, the aberrations on the axis and off the axis are wellbalanced, the distorting is extremely preferably corrected, the highcontrast in the high spatial frequency area is included as being obviousfrom the coma aberration, and it is possible to accomplish with the lowcost.

By use of this original reading lens, not only archiving favorablemethod and a device for reading an original in which a variation in SNratio is small when original information is a monochrome, but alsoarchiving a favorable method for reading an original and a device inwhich a variation in SN ratio of each color such as red, green, and blueis small even an original image is a full-color. The image formingapparatus, which is capable of forming a favorable image forming with alow cost and a compact, is able to be accomplished by use of this devicefor reading an original.

1. A reading lens comprising: five lenses including at least twopositive lenses and two negative lenses, wherein the five lenses includea positive first lens, a positive second lens, a negative third lens, anegative fourth lens and a positive fifth lens sequentially arrangedfrom the object side of the reading lens, the positive second lens andthe negative third lens are cemented as a single cemented lens having anegative refracting power, an aperture stop is disposed between thenegative third lens and the negative fourth lens, the negative fourthlens includes an aspherical lens, a curvature radius of a first surfaceof the aspherical lens on an object side of the aspherical lens is r1 a,a curvature radius of a second surface of the aspherical lens on animage side of the aspherical lens is r2 a, and r1 a and r2 a satisfy:1.4<r 2 a/r 1 a<2.3.
 2. The reading lens according to claim 1, wherein afocal length of an e line of the first lens is f1, a combined focallength of an e line of the reading lens is f, an average of a refractiveindex of a d line of all positive lenses is n convex, an average of arefractive index of a d line of all negative lenses is n concave, anaverage of an Abbe's number of all positive lenses is ν convex, anaverage of an Abbe's number of all negative lenses is ν concave and:0.54<f 1</f<1.14,−0.16<n convex−n concave<0.05, and18.11<ν convex−ν concave<32.13.
 3. An image reading device, comprising:an illumination system configured to illuminate an original; a readinglens configured to image a reflection light of an original image of theoriginal illuminated by the illumination system, the reading lenscomprising: five lenses including at least two positive lenses and twonegative lenses, wherein the five lenses include a positive first lens,a positive second lens, a negative third lens, a negative fourth lensand a positive fifth lens sequentially arranged from the object side ofthe reading lens, the positive second lens and the negative third lensare cemented as a single cemented lens having a negative refractingpower, an aperture stop is disposed between the negative third lens andthe negative fourth lens, the negative fourth lens includes anaspherical lens, a curvature radius of a surface of the aspherical lenson an object side of the aspherical lens is r1 a, a curvature radius ofthe aspherical lens on an image side of the aspherical lens is r2 a, andr1 a and r2 a satisfy:1.4<r 2 a/r 1 a<2.3; and a line sensor configured to photoelectricallyconvert the original image imaged by the reading lens for reading theoriginal.
 4. The image reading device according to claim 3, furthercomprising: a color separation unit configured to read information ofthe original image with a full range of colors.
 5. An image formingdevice, comprising: a photosensitive medium for forming an image bywriting an image information with a light scanning; and an image readingdevice comprising: an illumination system configured to illuminate anoriginal; a reading lens configured to image a reflection light of anoriginal image of the original illuminated by the illumination system,the reading lens comprising: five lenses including at least two positivelenses and two negative lenses, wherein the five lenses include apositive first lens, a positive second lens, a negative third lens, anegative fourth lens and a positive fifth lens sequentially arrangedfrom the object side of the reading lens, the positive second lens andthe negative third lens are cemented as a single cemented lens having anegative refracting power, an aperture stop is disposed between thenegative third lens and the negative fourth lens, the negative fourthlens includes an aspherical lens, a curvature radius of a surface of theaspherical lens on an object side of the aspherical lens is r1 a, acurvature radius of the aspherical lens on an image side of theaspherical lens is r2 a, and r1 a and r2 a satisfy:1.4<r 2 a/r 1 a<2.3; a line sensor configured to photoelectricallyconvert the original image imaged by the reading lens for reading theoriginal; and a color separation unit configured to read information ofthe original image with a full range of colors.